Double-break vacuum switch with bellows mounted movable bridging contact



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DOUBLE-BREAK VACUUM SWITCH WITH BELLQWS MOUNTED MOVABLE BRIDGING CONTACT Filed Nov. 18, 1964 5 Sheets-Sheet l in van tor-*3 L/d mes D. Cob/'ne,

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1966 J. D. COBINE ETAL DOUBLE-BREAK VACUUM SWITCH WITH BELLOWS MOUNTED MOVABLE BRIDGING CONTACT Filed NOV. 18, 1964 5 SheetsSheet 2 A I @E? M bl l irwe r7 tors: dames D. Cob/me Raymond /-/.Jo nston, y

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Nov. 1, 1966 J, D COBINE ETAL 3,283,101

DOUBLE-BREAK VACUUM SWITCH WITH BELLOWS MOUNTED MOVABLE BRIDGING CONTACT Filed Nov. 18, 1964 5 Sheets-Sheet 5 Inventors:

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United States Patent 3,283,101 DOUBLE-BREAK VAQUUM SWITCH WITH BEL- LOWS MOUNTED MGVABLE BRIDGING CUN- TACT James I). Cobine, Rexforrl, and Raymond H. Johnston, Cohoes, N.Y., assignors to General Electric Company, a corporation of New York Filed Nov. 18, 1964, Ser. No. 412,159 4 Claims. (Cl. 200-144) The present invention relates to an improved vacuum circuit interrupter characterized by high interrupting capacity in relation to its size and to the required circuit interrupting movement.

Vacuum switches, when new, are characterized by relatively high current interrupting capacity and relatively rapid recovery of dielectric strength on circuit breaking movement. These desirable characteristics may, in some instances, be gradually impaired as electrode erosion and other inherent effects of aging and use accumulate. In vacuum circuit interrupters of the type having low chopping current values, electrode erosion is usually inherent. This is because electrodes that have high vapor pressures and copiously produce conduction carriers during arcing are normally characterized by greater erosion than electrodes of refractory materials. The use of high vaporpressure electrode materials is consciously practiced to secure low current chopping values.

In accordance with the present invention, a vacuum switch is provided in which circuit break occurs over at least two series connected gaps. As described in more detail hereafter, mechanical elements are arranged to assure that the electrodes open the gaps in unison, and thereby provide essentially simultaneous dielectric strength recovery across the respective gaps. The energy required to be dissipated on circuit breaking movement is accordingly divided about equally between the gaps, providing a corresponding reduction in the tendency of each electrode to erode and a correspondingly longer electrode life.

More particularly, the present invention contemplates a vacuum type circuit breaker in which at least two fixed electrodes are located Within the vacuum envelope to define contact faces on a substantially common plane and in positions substantially symmetrical about an axis normal to that plane. A movable electrode is provided to bridge these fixed electrodes in the contact-making or circuit-making position and to define uniform gaps in relation to these fixed electrodes during and after contactopening movement. Resilient means, such as a resilient bellows or a caged spring is disposed between the movable electrode and the movable operating member and is effective in axial compression and bending in the circuit-making position to hold the electrodes in firm contact-making relationship despite tolerances associated with manufacturing operations and electrode Wear. As the operating member is moved to circuit-breaking position, the movable electrode is subjected to a force imparting largely translational motion to open the gaps substantially in unison and divide the voltage and electrode was substantially equally.

As above mentioned, electrode erosion is normally an integral part of the action of a vacuum interrupter that carriers current until essentially natural current zero. This erosion-together with the inherent difficulty of disposing the parts in a vacuum envelope in exactly aligned positions and retaining them in such positionsprecludes the use of a movable contact rigidly afiixed to the movable operating member. Through the accommodating action provided by the resiliently compressible and bendable elements provided in accordance with the present invention, the tolerances of the fixed contact members are taken up 3,283,101 Patented Nov. 1, 1966 in the contact-making position and substantially uniform electrode pressure is applied. Upon initial opening movement, the movable electrode moves largely in translational motion that initially opens the gaps in substantial unison to provide substantially equal division of voltage and electrode wear. The movable electrode ultimately comes to rest in a predetermined spaced position in relation to the fixed electrodes, at which position the movable electrode may have rotated or rocked somewhat from the contactmaking position. At this time, however, the two gap lengths are relatively large and any deviations from equal lengths do not result in significant differences in voltage or electrode wear.

It is therefore an object of the present invention to provide an improved multiple-break vacuum switch in which the respective gaps are formed in unison and divide the arcing energy on substantially an equal basis despite misalignment and contact erosion.

Still another object of the present invention is to provide an improved multiple-break vacuum switch in which the bridging member or movable electrode moves in substantially translational movement at the time of contact separation to form the gaps in substantial unison despite misalignment and contact erosion.

It is still another object of the present invention to provide an improved multiple-break vacuum switch that is simple in construction, reliable in operation, suitable for practical commercial manufacture, has long life, and in other respects is suitable for practical application on alternating current power systems and in other applications.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims. Our invention itself, however, together with further objects and advantages hereof, will best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a view in axial cross-section with parts in elevation of an illustrative embodiment -of the present invention using resilient bellows to support the movable contact member;

FIGURE 2 is a fragmentary view through the axis 22, FIGURE 1;

FIGURE 3 is a view in axial cross-section with parts in elevation of another embodiment of the present invention using a spiral spring and stop surfaces to support the movable contact member, the structure being shown in circuit-breaking position;

FIGURE 4 is a fragmentary view of the apparatus of FIGURE 3, along axis 4-4 and with parts in cross-sec tion; and, I

FIGURE 5 is a fragmentary view of the apparatus of FIGURE 3, like FIGURE 3 but showing the contactmaking position of the parts.

In FIGURE 1, of the drawing there is shOWn generally at 1 a vacuum envelope in whichthe switch operating parts are disposed. This envelope is defined by metallic annular end cap 2, having an annular flange 3. Metallic sleeve 4, preferably of fernico, is welded or brazed to flange 3 and, at the other end thereof is embedded in flared glass sleeve 5, as shown. A second sleeve 6, preferably of fernico, is embedded in the opposite end of glass sleeve 5 and is itself welded to annulus sealing ring 7, which is in turn welded to a similar sleeve 8, both of which are preferably of fernico. The latter is embedded in the cylindrical glass sleeve 9, into which is also embedded cylindrical sleeve 10, also preferably of fernico. The latter is welded or otherwise aflixed to annular end cap 11 to complete the envelope except for the electrode suporting parts. It will be observed that the envelope is symmetrical about the axis X X and, when properly sealed at its opposite ends and exhausted, provides the vacuum space shown generally at 12.

A pair of fixed electrode rods 13 and 14, carrying electrodes and 16, respectively, extend outside the vacuum space 12 through end cap 11 as seen in FIGURE 1. The exterior ends of the electrode rods 13 and 14 are connected to the circuit to be interrupted (not shown). Inside the vacuum space, electrodes 15 and 16 have contact faces 17 and 18, respectively, located on a common plane normal to the longitudinal switch axis XX. The remainder of the surfaces of contacts 15 and 16 other than the contact faces 17 and 18, are smoothly curved surfaces, as shown, to provide a maximum uniformity of field upon contact-breaking condition.

The electrode rods 13 and 14 are supported from the annular end cap 11 by the cylindrical glass insulating sleeves 19 and 20, respectively. The end cap 11 has two spaced circular holes 21 and 22 adapted to receive and clear the electrode rods 13 and 14, respectively. Sleeves 23 and 24, preferably of fernico, are afiixed to the margins of these holes, as shown, and are embedded in the glass sleeves '19 and 20, respectively, to support the same. Metal sleeves 25 and 26, respectively are embedded in the exterior ends of sleeves 19 and respectively. These are preferably of fernico and are afiixed at their opposite ends to the metal annular end caps 27 and 28, respectively, to close the vacuum space and provide insulating supports for the respective electrode rods 13 and 14.

End cap 2 has a central cylindrical opening 29 therein. A metallic sleeve 30 is affixed to the margin of this opening by welding or other suitable means and at its opposite end receives the bellows 31, which is made of resilient metal, such as stainless steel. of the bellows 31 is aflixed to themetal sleeve 32, which in turn is welded or otherwise affixed to the end disk 33 of the movable operating member 34. It will be noted that the elements 2, 30, 31, 32 and 33 close the actuating end of the vacuum space 12. The movable operating member 34 is free to move back and forth along the axis XX as indicated by arrow'35. In the position of maximum inward movement, as hereinafter described, this member provides a circuit-making engagement of the electrode parts. In the position of maximum outward movement, as hereinafter described, this member provides a circuit-opening position of the electrode parts.

End disk 33 receives bellows 36 on its interior face. These bellows are made of resilient metal, preferably stainless steel. They are aflixed to the sleeve 37 at their interior end as seen in FIGURE 1, which sleeve is attached to the annular plate 38, as shown. Annular movable electrode 39 is attached to plate 38 by bolts or other suitable means (not shown). Electrode 39 defines an annular face 40 disposed in a plane and adapted to mate with the faces 17 and 18 of the fixed electrodes to bridge the same and establish contact therebetween.

The arrangement of the electrodes 15, 16, and 39 is shown in the further fragmentary cross-sectional view of FIGURE 2. It will be noted from FIGURES l and 2 that the electrode rods 13 and 14 and electrodes 15 and 16 are symmetrically located in relation to the switch axis XX. Moreover, the faces 17 and 18 are on a common plane normal to this axis. It will further be noted that the movable operating member 34 moves along its axis and that the movable electrode 39 is symmetrical in relation to this axis. This locates the center of mass or centroid of the movable electrode on the axis XX. It follows that when the movable operating member 34 is moved from the closed or circuit-making position to the open or circuit-breaking position over the short circuitbreaking distance and with the rapid speed of circuit interruption, the inertia of the electrode 39 and the associated parts does not tend to tilt that member momentarily as the gap is opened in either direction and thus tends to open the gaps between the electrodes in unison.

The annular flange member 7 terminates at its interior edge in a cylindrical flange, to which are affixed the The opposite end' 4 opposed curved conducting shields 41 and 42. These provide surfaces upon which the evaporated electrode metal can condense without impairing the insulating integrity of the glass portions of the vacuum envelope.

When the movable operating member 34 is in the closed or circuit-making position, the movable electrode 39 assumes the position shown in the dotted lines of FIGURE 1. At this time the movable operating member 34 has been moved further inwardly than the actual movement of the movable electrode 39. The difference in movement is taken up by compression of the bellows 36 which thereby imparts a resilient force holding the movable electrode 39 against the fixed electrodes 15 and 16. This engagement under pressure assures a good conductive path between the electrodes 15, 39 and 16 and effective electrical conduction therebetween. Substantially equal pressure is imparted to the two fixed electrodes because of the relatively small bending spring constant of the bellows as compared to the compression spring constant.

When the circuit is to be opened, the movable operating member 34 is moved in the open or circuit-breaking direction ultimately reaching the point shown in the solid lines of FIGURE 1. Initially, the movable electrode 39 does not move, since the movement of the operating member 34 merely serves to relieve the spring pressure associated with the prior compression of the bellows 36. When this compression is relieved, however, the bellows extend in response to the inertial resistance to movement by the electrode 39 and parts 37 and 38, which expansion gives rise to a force tending to draw the electrode 39 in the circuit-breaking direction. The electrode 39 accelcrates in this and ultimately moves to the position shown in the solid lines of FIGURE 1.

The electrodes 15, 1 6, and 39, or at least some of them, are made of a material that effectively produces conduction carriers in response to the electric field and heat of the arcs formed when the contacts separate. The particular materials used for this purpose form no part of the present invention. Electrodes made of or containing tin are illustrative of such materials. These and others are described and claimed in United States Patent No. 2,975,256 to Lee and Cobine. When the contacts separate the conduction carriers in the form of ionized vaporized electrode material and otherwise serve as effective conductors of the electric current. Because of the copious supply of these conductors, the current is carried across the two gaps between electrodes 15 and 39 and electrodes 16 and 39 with a comparatively small voltage drop. At this particular time, the voltages across the respective gaps are not critically dependent upon their respective spacings.

When the natural current zero is approached in the circuit to which the electrode rods 13 and 14 are connected, the supply of conduction carriers in the gaps is reduced and ultimately becomes insuflicient to continue the arcs. Once one of the arcs is broken, the current flow discontinues and a recovery voltage appears across the electrodes 15 and 16. It is essential that the arcs do not restrike under the influence of this recovery voltage. The effectiveness of the interrupter in withstanding this recovery voltage is determined by the total gap length, the extent conduction carriers are present in the respective gaps, and the condition of the electrodes. If, immediately prior to arc interruption, the two gaps are of substantially identical length and the conditions of the electrodes are such that the conduction carriers disappear from the gaps essentially simultaneously, the recovery voltage divides essentially equally between the gaps. The ability of the interrupter to withstand the recovery voltage is then essentially twice that associated with a similar gap in a single gap switch. Conversely, if the gaps are of unequal length, the electrodes are of unlike condition, or the conduction carriers are unequally distributed, the recovery voltage will divide unequally and the ability of the interrupter to withstand such voltage may be less than twice that associated with a single gap.

The apparatus of FIGURE 1 tends to provide the most favorable simultaneous opening of the gaps between the electrodes when the operating member 34 is moved from the circuit-making position to the circuit-breaking position. Under the compression of bellows 36, the movable electrode 39 remains in contact-making position until the member 34 has executed an initial movement at least sufficient to eliminate the compression on bellows 36. Thereafter the movable electrode 39 moves to the circuit opening direction under the force applied by the bellows 36 as it extends. If the electrodes 15 and 16 are not in precise alignment with electrode 39or any of these electrodes have worn unequally-the effect is merely to impart to the electrode 39 an initial tilt at the moment that the bellows 36 exerts its first net force tending to move electrode 39 to the right. The ability of the bellows to flex resiliently permits this initial positioning of the electrodes. Thereafter, as the bellows pulls the electrode 39 in the circuit-opening direction, the tendency is to move it in largely translational movement giving rise to a substantially uniform increase in the two gaps.

The initial movement of the movable electrode 39 is largely translational because the design of bellows 36 is such that the torque associated with flexure of bellows 36 under normal degrees of electrode misalignment is rela tively small in relation to the moment of inertia of the assembly 39, 38 and 37 about an axis transverse to axis XX. By relatively small, it is meant that the translational forces of the bellows exceed the bending forces by at least approximately one order of magnitude, or a ratio of at least approximately ten to one. The rotational acceleration of the movable electrode 39 is accordingly relatively small. In contrast, the net translational force exerted on the movable electrode 39 at the time of circuitbreaking movement is relatively large in relation to the inertia of the assembly 39, 38, and 37. This gives rise to large translational acceleration under the action of the bellows 36. The net effect is to continue the initial tilt of the movable electrode 39 as the gaps are initially opened, to cause the two gaps to enlarge in unison and to define spaces of like capacity and dielectric strength, thus providing an interrupter that is capable of withstanding essentially twice the recovery voltage associated with a single gap. Ultimately, the rocking or tilt of the movable electrode required by the fixed electrodes disappears, and the movable electrode assumes the full opened rest position. At this time, the gaps are not of identical length (assuming some fixed contact misalignment), but the proportional difference is not sufficiently great to create substantial inequality of voltage and electrode wear.

In the alternative embodiment of the present invention shown in FIGURES 3-5, inclusive, the vacuum envelope 43 is of metal construction to define the vacuum space 44. The insulating bushings 45 and 46 are carried by the top cap 49 of the envelope 43 and support, respectively, the fixed electrodes 47 and 48. Each of these electrodes carries an arc shield 50 and 51, respectively, serving to shield the interior insulating surfaces of the bushings 45 and 46 from the evaporated metal formed during each arc interruption. It will be noted that the fixed electrodes 47 and 48 have contact faces disposed in a horizontal plane and symmetrically positioned about the axis 5252.

The movable electrode 53, FIGURE 3, is a fiat bar of conducting material symmetrically disposed in relation to axis 5252 and having faces that seat against the faces of the fixed electrodes 47 and 48 to bridge the same and establish a conducting path in the circuit making condition. The centroid or center of mass of this bar is substantially on axis 52-52. The electrode 53 is mounted on and carried by a support frame defined by the members 54 and 55, to which it is attached by bolt 56. Member 55 has a central circular opening 57 which defines a socket into which the spiral compression spring 6 58 fits, as shown. The opposite end of this spring seals on the head portion 59 of the movable operating member. This head member has a center enlargement that anchors the spring 58 in position.

The movable operating member 60 is attached to the head portion 59 by the bracket 61 which is in turn affixed to the plate 62, to which the mounting socket-like member 63 is aiiixed. The imperforate bellows 64 extends from the plate 62 to the bottom cap 65 of envelope 43 to complete the vacuum enclosure. Fixed sleeve 66 serves as a guide for the movable operating member 60, and spring 67 serves to bias that member to the down or circuit-breaking position.

Movable operating member 60 is lifted against the bias of spring 67 (and spring 58, when the contacts are engaged) by the external operating member which is moved by suitable actuating means (not shown).

The parts 63, 68, 55, and 54 define a lost motion connection between the movable electrode 53 and the movable operating member 60 and hold the spring 58 in caged position. This connection may be traced as follows. The socket-like member 63 is afiixed to the operating member 65 as above described. As illustrated in FIGURE 4 the portions 69 of this member overlay the outwardly extending foot portions of member 68, thereby anchoring the member 63 for movement in unison with the movable operating member 60. The member 68 has outwardly extending cars 70 which define lower stop surfaces 71 which are in overlaying relationship with the stop surfaces 72 formed by the inturned foot portions of the member 55, as shown. As previously indicated, the member 54 is afi'ixed to the member 55.

It will be noted that in the contact-breaking position of FIGURE 3, the spring 58 forces the movable electrode 53 upwardly in relation to the movable operating member 60. The stop surfaces 7l-72 accordingly engage, restraining the movable electrode 53 against the spring force.

When the movable operating member 60 is in the circuit-making position as shown in FIGURE 5, the movable electrode 53 bears against fixed electrodes 47 and 48. At this time the fixed electrodes 47 and 48 take up the pressure of spring 58, compressing the same, and moving the stop surfaces 7172 out of engagement with each other.

As the operating member 60 is brought down from the circuitmaking position shown in FIGURE 5 to the circuit-breaking position shown in FIGURE 3, the compression of spring 58 initially holds the movable electrode 53 against the electrodes 47 and 48. Since the spring relatively freely accommodate tilting movement of the electrode 53, this condition maintains even if the electrodes are somewhat misaligned. Further movement of the operating member 6t) in the down direction relaxes spring 58 and ultimately gives rise to engagement of the surfaces 71-72. The movable electrode 53 is now brought down and opens the gaps with electrodes 47 and 48.

If the electrodes 47, 48 and 53 are in exact alignment, the stop surfaces 7172 engage on both sides and there is no tilting or rocking torque exerted at any time on the electrode 53. In this ideal condition, therefore, the sole movement of that electrode is translational movement and at all times the gaps between the electrodes are the same. A more typical condition, however, is with some misalignment of the fixed electrodes, due to error in initial manufacture or to the subsequent change in shape or position of the electrodes. Whatever the cause, the misalignment causes the electrodes 53 to have some degree of tilt in relation to the direction of movement of the operating member 60 at the instant the movement of member 60 commences. This tilt is accommodated by the spring 58 with only a relatively small resisting torque, and is held while the operating member 60 moves down. As the downward movement of the operating member 60 continues, one or the other set of stop surfaces 71 72 engages,

at which time a positive force is applied from the operating member 60 to the electrode 53. The electrode 53 is then subjected both to a translational force and to a torque tending to restore it to the aligned position in relation to the operating member 60, the electrode 53 then moves down and rocks back towards the aligned position, and ultimately the other stop surfaces 7172 engage to pull the electrode 53 down to the final position.

While the electrode 53 is subjected to a restoring torque from a tilted position, there is a substantial moment of inertia of the assembly 53, 54, 55 that resists this torque and prevents an immediate restoration of the aligned position of this electrode. The resulting angular acceleration is relatively small so that electrode 53 moves in largely translational movement in response to the force exerted by thestop surfaces 7172 that first engage. The gaps accordingly initially open substantially uniformly.

While the foregoing examples of the present invention are of the type using a pair of fixed electrodes, it will be understood that more than two such electrodes may be used. In such instance, the fixed electrodes are disposed uniformly about an annulus concentric with the axis of movement of the movable operating member, and the movable electrode has a contact face adapted to engage each of the fixed electrodes, respectively. The symmetry of the interrupter is then the same as with only two fixed electrodes.

While we have here described only specific enibodiments of the present invention it will, of course, be understood the modifications and alternative constructions may be made without departing from the principles herein set forth. We therefore intend by the appended claims to cover the modifications and alternative constructions falling with their true spirit and scope.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A double-break vacuum switch adapted to effect simultaneous contact closing and opening operations between two pairs of serially connected closable gaps upon actuation and comprising:

(a) An evacuable envelope, at least a portion of which (d) A movable electrode support rod hermetically sealed through a second wall of said envelope, opposed to said first wall, by means of a first resilient vacuum-tight bellows sealed to said envelope at its one end and to the periphery of a flange on said movable electrode rod at its other end,

(dd) The interior of said first bellows being open to ambient pressure;

(e) A movable annular electrode member having a diameter and radial thickness sufficient to allow said annular electrode to make contact with the arcing surfaces of said fixed electrodes when urged into circuit making position to rest in a plane normal to said longitudinal axis, the centroid of said movable annular electrode being along said longitudinal axis, and a (f) A second flexible bellows affixed at one end to a disc rigidly aflixed to said movable electrode rod and at the other end thereof to said movable annular electrode and being the only mechanical support and constraint connection between said movable electrode and said movable electrode support rod,

(ff) Said second bellows being characterized in exhibiting a ratio of forces of longitudinal motion to forces of rotational motion upon circuit opening as to allow said movable electrode to be withdrawn from said fixed electrodes at an angle to a plane'which is normal to said longitudinal axis, whereby in the event of irregularities of contact surfaces, both of said gaps are simultaneously opened upon actuation of said movable electrode support rod in a circuit opening direction. 2. The vacuum switch of claim 1 wherein the ratio of forces in said second flexible bellows is at least 10 to l. 3. The vacuum switch of claim 1 wherein the diameter of said second flexible bellows is substantially the same as the mean diameter of said annular movable electrode. 4. The vacuum switch of claim 1 wherein the ratio of forces in said second flexible bellows is at least 10 to 1 and the diameter thereof is substantially the same as the mean diameter of said annular movable electrode.

References Cited by the Examiner UNITED STATES PATENTS 2,908,780 10/ 1959 Walters 200144 2,981,813 4/1961 Jennings 200-144 3,036,180 5/1962 Greenwood 200144 ROBERT K. SCHAEFER, Primary examiner.

ROBERT S. MACON, Examiner. 

1. A DOUBLE-BREAK VACUUM SWITCH ADAPTED TO EFFECT SIMULTANEOUS CONTACT CLOSING AND OPENING OPERATIONS BETWEEN TWO PAIRS OF SERIALLY CONNECTED CLOSABLE GAPS UPON ACTUATION AND COMPRISING: (A) AN EVACUABLE ENVELOPE, AT LEAST A PORTION OF WHICH IS COMPOSED OF INSULATING MATERIAL TO ELECTRICALLY ISOLATE RESPECTIVE ELECTRODE LEADS; (B) A PAIR OF FIXED ELECTRODE SUPPORT RODS INSULATINGLY AND HERMETICALLY SEALED THROUGH A FIRST WALL OF SAID ENVELOPE, (BB) SAID ELECTRODE SUPPORT RODS BEING PARALLEL WITH ONE ANOTHER AND WITH THE LONGITUDINAL AXIS OF SAID ENVELOPE, AND (C) A FIXED ELECTRODE MOUNTED UPON THE INNER END OF EACH OF SAID SUPPORT RODS, EACH OF SAID FIXED ELECTRODES CONTAINING AN ARCING SURFACE DISPOSED IN THE SAME PLANE WHICH IS NORMAL TO SAID LONGITUDINAL AXIS (D) A MOVABLE ELECTRODE SUPPORT ROD HERMETICALLY SEALED THROUGH A SECOND WALL OF SAID ENVELOPE, OPPOSED TO SAID FIRST WALL, BY MEANS OF A FIRST RESILIENT VACUUM-TIGHT BELLOWS SEALED TO SAID ENVELOPE AT ITS ONE END AND TO THE PERIPHERY OF A FLANGE ON SAID MOVABLE ELECTRODE ROD AT ITS OTHER END, (DD) THE INTERIOR OF SAID FIRST BELLOWS BEING OPEN TO AMBIENT PRESSURE; (E) A MOVABLE ANNULAR ELECTRODE MEMBER HAVING A DIAMETER AND RADIAL THICKNESS SUFFICIENT TO ALLOW SAID ANNULAR ELECTRODE TO MAKE CONTACT WITH THE ARCING SURFACE OF SAID FIXED ELECTRODES WHEN URGED INTO CIRCUIT MAKING POSITION TO REST IN A PLANE NORMAL TO SAID LONGITUDINAL AXIS, THE CENTROID OF SAID MOVABLE ANNULAR ELECTRODE BEING ALONG SAID LONGITUDINAL AXIS, AND (F) A SECOND FLEXIBLE BELLOWS AFFIXED AT ONE END TO A DISC RIGIDLY AFFIXED TO SAID MOVABLE ELECTRODE ROD AND AT THE OTHER END THEREOF TO SAID MOVABLE ANNULAR ELECTRODE AND BEING THE ONLY MECHANICAL SUPPORT AND CONSTRAINT CONNECTION BETWEEN SAID MOVABLE ELECTRODE AND SAID MOVABLE ELECTRODE SUPPORT ROD, (FF) SAID SECOND BELLOWS BEING CHARACTERIZED IN EXHIBITING A RATIO OF FORCES OF LONGITUDINAL MOTION TO FORCES OF ROTATIONAL MOTION UPON CIRCUIT OPENING AS TO ALLOW SAID MOVABLE ELECTRODE TO BE WITHDRAWN FROM SAID FIXED ELECTRODES AT AN ANGLE TO A PLANE WHICH IS NORMAL TO SAID LONGITUDINAL AXIS, WHEREBY IN THE EVENT OF IRREGULARITIES OF CONTACT SURFACES, BOTH OF SAID GAPS ARE SIMULTANEOUSLY OPENED UPON ACTUATION OF SAID MOVABLE ELECTRODE SUPPORT ROD IN A CIRCUIT OPENING DIRECTION. 